Journal of Computations & Modelling, vol.4, no.1, 2014, 39-51
ISSN: 1792-7625 (print), 1792-8850 (online)
Scienpress Ltd, 2014
Electric Machine Experimental Monitoring System
based on Labview Environment
Panayiotis Michalopoulos1, Christos Kalogrias2,
Fotis D. Kanellos3 and George J. Tsekouras4
Abstract.
It is widely accepted that contemporary scientific experimentation on electrical
machines requires extensive measurements and acquisition of various data. The
equipment used for this purpose is usually quite expensive and dedicated to a specific
application. In this paper the development of a programmable, versatile and
inexpensive system based on Labview environment is described. This is able to
perform an essentially limitless number of simultaneous measurements on any kind of
experimental or applied installation. Furthermore, the same system is able to perform
extensive signal conditioning and processing, in order to automatically produce
complex graphs and facilitate the drawing of conclusions. Finally, the same system
may actively control electrical equipment allowing for even more complex
experiments to be performed. In this case, an ac/ac converter supplies power to an
electric motor. Six differential voltages and six currents are measured and recorded in
real time, while power, total harmonic distortion etc are calculated, in order to
determine whether the use of the ac/ac converter is efficient or not.
Keywords: Data acquisition, LabView, measurement system, induction motor, power
electronics.
1
CDR (Eng) Hellenic Navy, Hellenic Naval Academy, Terma Hatzikiriaku, Piraeus, GR18539, Greece
E-mail:panos.michalo@gmail.com
2
LCDR (Eng) Hellenic Navy, Hellenic Naval Academy, Terma Hatzikiriaku, Piraeus, GR18539 Greece
E-mail:ckalogr@gmail.com
3
Lecturer, Production Engineering & Management Department, Technical University of
Crete, Chania, GR-73100, Greece
E-mail: fkanellos@dpem.tuc.gr
4
Lecturer, Hellenic Naval Academy, Terma Hatzikiriaku, Piraeus, GR-18539 Greece
E-mail: tsekouras@snd.edu.gr
40
Electric Machine Experimental Monitoring System
1. Introduction
The basis of any scientific experimentation is the ability to perform measurements.
The simplest phenomena on electrical machines are related to their steady-state
behavior. These can easily be studied with the use of common instruments like Vmeters, A-meters, oscilloscopes etc. However, when more complex phenomena need
to be studied like transient behavior, notches and harmonic distortion, then more
sophisticated equipment is required. Such instruments are multichannel oscilloscopes,
measurement recorders etc, which are very expensive and many times prove to be
inadequate.
The introduction of data acquisition devices solved all these problems by offering
accurate and high-speed equipment that can use regular PCs to store and process very
large amounts of measurements. Furthermore, they can provide interactive and smart
collection of data, accelerating and facilitating the work of the researcher.
2 What is a DAQ?
Today, commercial Data AcQuisition devices (DAQs) allow for the simultaneous
input of 16, 32 or more voltages at sampling speeds that range from a few kHz to
many GHz. Conversion from analog to digital is not a problem, because the resolution
provided can be quite high (24 bits or more). This data may be processed extensively
in a computer to provide real-time results with no effort.
Moreover, DAQ devices may also output several voltages to drive analog actuators.
This way, very complex experiments can be implemented. In addition to the above,
numerous digital inputs and outputs are also provided, allowing for multiple triggers,
switch activation etc.
Such multiple analog and digital input / output systems, with the processing power
provided by computers, can be networked together to form a cluster of virtually
infinite measuring potential.
There are several ways to program a DAQ device, using general purpose languages
like C++ or specific graphic environments like LabVIEW. The latter allows for the
creation of the so called “virtual instruments”, which can be fully customized. All
dataflow from measurement and data processing to data storage, results presentation
and signal output is programmed using graphic blocks, much like Matlab’s Simulink.
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
41
3 Developed DAQ System
3.1 The initial problem of energy efficiency study of topologies for
power converters & electrical motors
Modern warships are equipped with many induction motors of different nominal
powers ranging from a few hundred Watts up to several MW. Most of them are threephase squirrel type induction motors, with the exception of small one-phase motors
used in accommodation spaces and large multi-phase propulsion motors [1]. The
performance of the induction motor is quite satisfying when it is operating close to its
nominal power and speed [2].
However, its high starting current and low starting torque drastically reduce its
efficiency, especially if the motor repeatedly starts and stops only to run for short time
intervals. Electrical equipment manufacturers state that the use of power electronics is
the solution to achieve energy saving [3]. This is true because power electronics
significantly limit the starting current and its respective losses. They can also increase
the motor’s efficiency by supplying it with variable voltage and frequency, in order to
drive it on its optimum operating point for each load. This is calculated by a
specialized automatic control system.
On the other hand, power electronics cause power quality problems, like harmonic
injection. The existence of current and voltage harmonics in their output causes
additional power loss on the induction motor, because of magnetic hysteresis losses,
eddy currents on the core and of skin effect on copper windings. Also, the existence
of current harmonics in their input causes additional power loss on the cables and busbars, because of skin effect and operational problems in other electrical equipment.
Some of them are inaccurate operation of automatic control systems, flickering
phenomenon at fluorescent lamps etc.
3.2 The prototype data acquisition system
In previous work [4], an experimental setup was implemented to verify and
approximately quantify the efficiency of driving a motor with a power-electronics
converter. In this setup, a three-phase squirrel induction motor is driving an
electrodynamometer which represents the mechanical load (i.e. a pump, a fuel oil
42
Electric Machine Experimental Monitoring System
separator etc). This motor is powered by a regular three-phase power supply, either
directly or through an AC/DC/AC electronic converter. The basic topology and a
photo of the experimental setup are shown in Figures 1 and 2 respectively.
All six voltages are measured, in respect to the neutral, using differential voltage
probes with a transformation ratio of 1:200 (see Fig. 3). Also, all six line currents are
measured using current probes (clamps) with a transformation ratio of 1A:500 mV
(see Fig. 4). In order to amplify the weak current signal, each line is turned over the
clamp four times.
All these signals are collected and properly sampled by the heart of the system,
which is a data acquisition USB device (see Fig.5), with 16 multiplexed analog inputs
and a maximum combined sampling rate of 200 KS/s [5].
In this setup, 12 inputs are used and sampled at 13 kHz each. From these inputs,
measurements are acquired, processed, displayed and stored in bunches of 500
samples per input.
Public supply
400/230V, 50Hz
Power supply (inverter & stabilizer) 9 V d.c. for probes
prob
es
EMS8821-13
power
supply
MITSUBISHI
9V
d.c.
VVVA
FR-E540-0.4K~
EC
A
A
~
EMS8219-00
electrodynamom
eter
Lab-volt EMS882105 squirrel
induction motor
VVVA
9V
d.c. 6015
National Instr. DAQPad
A
EL
M~3
A
Figure 1. Detailed block diagram of the experimental setup
(the supply of the excitation winding of the electrodynamometer is omitted for simplicity).
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
43
Figure 3. HAMEG Instruments HZ-100
differential voltage probe.
Figure 4. Chauvin Arnoux E3N current probe.
Figure 2. Photo of the experimental
topology.
Figure 5. National Instruments DAQPad 6015
data acquisition device.
The inputs are multiplexed, meaning that they are not sampled simultaneously,
which could lead to erroneous results. However, since the time required to receive a
sample from every input is much smaller than the 0.02sec – that correspond to the
50Hz frequency of the mains – the measurements may be considered simultaneous.
All the above are adjusted and controlled by a PC connected to the DAQ device.
This PC is programmed using a block-diagram style environment called LabVIEW
(see Fig.6). With this one can create very versatile custom views of data
representation and control called Virtual Instruments (see Fig.7).
44
Electric Machine Experimental Monitoring System
Figure 6.
LabVIEW algorithm.
Figure 7.
Virtual Instrument showing instant voltages, currents and power per phase.
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
45
The algorithm created here performs the following:
 Virtual presentation and data storage of instant line-to-neutral voltages vi(t), of
instant line currents ii(t) and of instant power pi(t) for the three phases i=a,b,c of the
converter input and the converter output with respect to time t (see Fig. 6). Taking
into consideration the transformation ratio of differential voltage probes AV, the
transformation ratio of current probes AI and the number of turns at the clamps
(turns), the instant power pi(t) is then calculated as:
 A  i t  
pi  t    AV  vi  t     I i  i=a, b, c (1)
 turns 
 Virtual presentation and data registration of root mean square (R.M.S.) line-toneutral voltages Vi , R.M.S. of line currents Ii and of active power Pin-i for the
three phases i=a,b,c of the converter input and the converter output with respect to
time (see Fig.8). The respective calculations for R.M.S. line-to-neutral voltages are
realized as:

Vi 
t2
1
  vi2  t   dt
t2  t1 t1
T
k T t2 t1


NT k  NT k  NT
Vi 

Vi 
1 k NT 2
T
  vi  i   

T i 1
k  NT
1 NT 2
  vi  i  
NT i 1
Where t2-t1=k∙T, k is an integer number and T is the period of the three-phase
supply voltage Va(t)- Vb(t)- Vc(t). Because of the multiplication factor AV of the
voltage probe, finally the respective values of R.M.S. voltages are equal to:
1 NT 2
Vi  AV 
  vi  i   i=a, b, c (2)
NT i 1
46
Electric Machine Experimental Monitoring System
Figure 8. Virtual instrument showing root mean square values of line-to-neutral voltages,
line currents and active power per phase.
Similarly, the R.M.S. line currents are calculated taking into consideration the
transformation ratio of current probes AI and the number of turns at the clamps
turns:

t2
1
Ii 
  ii2  t   dt
t2  t1 t1
T
k T t2 t1


NT k  NT k  NT

AI
1 NT 2

  ii  i   i=a, b, c
…  Ii 
turns NT i 1
(3)
Respectively, the active powers per phase are calculated taking into consideration
the respective transformation factors of the probes:

Pi 
t2
1
  vi  t   ii  t   dt
t2  t1 t1
T
k T t2 t1


NT k  N T k  N T

…  Pi 
AV  AI NT
  vi  i    ii  i  
turns  NT i 1
i=a, b, c (4)
The apparent power Stot and the active power Ptot are calculated using the following
equations:
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
Stot 
Ptot 

Vi  Ii
(5)

Pini
(6)
i  a ,b ,c
i  a ,b,c
47
These calculations are used on the converter input and output measurements.
More parameters are then calculated. These are the power losses at the converter
Pconv_losses, the supply power factor cosφsupply (ignoring harmonic influences) etc:
Pconv _ losses  Ptot _ in _ inverter  Ptot _ out _ inverter (7)
cos supply 
Ptot _ in _ inverter
Stot _ in _ inverter
(8)
3.3 Equipment of the experimental system
The experimental setup has been developed in the Electric Circuits Laboratory of
the Hellenic Naval Academy.
The parts used are the following:
 a Lab-Volt EMS 8821-13 three-phase power supply with a variable output of 0 ÷
380V via auto-transformer, 3A/50Hz and a circuit breaker. This represents the
constant voltage supply of the motor.
 a Lab-Volt EMS 8821-05 three-phase squirrel induction motor with 175W
mechanical power, 380V, 0.52A, 50Hz, 1360rpm.
 a Lab-Volt EMS 8219-00 electrodynamometer with 0÷3N∙m torque and
0÷3000rpm rotational speed. The power supply of the excitation supply is:
220÷240V, 50Hz, 0.9A via a four-diode rectifier. It represents the mechanical load
of the motor.
 a HIOKI 3404 digital rpm counter with a measurement range of 30 ÷ 99.990rpm.
 a MITSUBISHI FR-E540-0.4K-EC AC/DC/AC converter, with 0.4kW active
power, 400V (380V÷480V) at 50/60Hz three-phase input voltage with permissible
AC voltage fluctuation 325 to 528V and frequency ±5%, rated output capacity
1.2kVA at 440V, three-phase output voltage 400V (380÷480V) at 50/60Hz [7].
48
Electric Machine Experimental Monitoring System
 twelve isolated 12Vdc/1A power supplies electronically stabilized and protected
from overcurrent and overheat.
With this equipment another variable that can be calculated is the output load
power Pout , which is related to the torque Ts and the mechanical rotational speed a as
follows:
Pout  Ts    Ts [N  m] 
a [R.P.M.]
60
(9)
After that, the total system efficiency , which is the ratio between the output load
power Pout and the input power Pin can be estimated:

Pout
Ptot _ in _ inverter
(10)
Even more variables can be calculated such as power saving, spectrum analysis,
total harmonic distortion etc.
4 An indicative experiment
The steady state energy saving problem of a three-phase squirrel induction motor is
studied in three cases:
 without power electronics converter (scenario 1),
 with power electronics converter, but without any special frequency regulation
(output converter voltage frequency equals to 50 Hz) (scenario 2),
 with power electronics converter, with voltage-frequency regulation with respect to
nominal output mechanical load (scenario 3).
The output mechanical load of electrodynamometer ranges between 0÷120W with
20W steps. The values of the 6 line-to-neutral voltages and 6 line currents of the three
phases are measured with the data acquisition (DAQ) system, the rotor speed of the
electrodynamometer with the HIOKI 3404 digital rpm counter and the torque with the
electrodynamometer’s indicator. The results are summarized in the following Figures
9 and 10.
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
49
60%
1800
1600
50%
1400
40%
1000
n [%]
a [R.P.M.]
1200
800
scenario 1
scenario 2
scenario 3
Poly. (scenario 1)
Poly. (scenario 2)
Linear (scenario 3)
600
400
200
30%
scenario 1
scenario 2
scenario 3
Poly. (scenario 1)
Poly. (scenario 2)
Poly. (scenario 3)
20%
10%
0%
0
0
20
40
60
80
Pout [W]
100
120
140
0
20
40
60
80
Pout [W]
100
120
Figure 2. Mechanical power load Pout vs Figure 3. Mechanical power load Pout total
motor speed a, for (1) without power motor efficiency  , for (1) without power
power electronics
converter,
electronics converter without frequency electronics
converter
without
frequency
(3)
power
electronics
electronics
converter,
regulation, (3)
(2)
with power
with
electronics regulation,
converter and voltage-frequency regulation.
with
(2)
with
power
converter and voltage-frequency regulation.
From the results, it can be derived that the total system efficiency is worse when a
power converter is used without any frequency regulation. When voltage-frequency
regulation is used, the total system efficiency is better for small mechanical load. That
is because the losses of the converter harmonics are smaller than the power losses of
the motor operating at its nominal slip point.
5 Conclusions
DAQ devices are invaluable instruments for recording and utilization of large
amounts of measurements, when studying the transient and steady-state behavior of
electric equipment. Especially in the modern warships, which become more and more
all-electric, it is of particular interest to record simple parameters, like currents and
voltages. From them more values, like efficiency, can be calculated. This way,
equipment can be operated at low cost and its reliability can be increased.
140
50
Electric Machine Experimental Monitoring System
6 Future steps
In the future the following will be implemented:
 The measurements of the mechanical load and the rotor speed will be added to the
data acquisition system. This way all necessary measurements will be recorded
simultaneously, increasing precision.
 The measurements of the voltages and currents can be utilized for the study of the
supply’s and motor’s harmonic behavior.
 The transient phenomena will also be studied in different scenarios and energy
saving results will be produced for different operating periods of the motor and
variable torque profiles.
 The measurement process will be enhanced with emphasis to parameter calibration,
such as sampling rate etc.
 The measurement system will be programmed to automatically be self-calibrated to
the bias values and the actual transformation rations of the voltages and the currents
probes.
7 Acknowledgements
The authors would like to thank Dr. I.K. Hatzilau, Emeritus Professor at the Hellenic
Naval Academy, for his overall contribution to the configuration of the Electric
Circuits Laboratory at the Hellenic Naval Academy.
Nomenclature
DAQ: Data AcQuisition system
References
[1] F. Terrien, S. Siala and P. Noy: Multiphase induction motor sensorless control
for electric ship propulsion, 2nd international conference on power Electronics,
machines and drives, PEMD-2004
P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G.J. Tsekouras
51
[2] Th. Wildi: Electrical Machines, Drives, and Power Systems, 5th Edition,
Pearson Prentice Hall, New Jersey, 2002, p. 860
[3] St. Rudell: ABB Review special report motors and drives: Improving motor
efficiency, 1st edition, 2010.
[4] P. Michalopoulos, Ch. Kalogrias, F.D. Kanellos and G. J. Tsekouras:
Experimental investigation of energy saving using power electronics to
operate ship induction electric motors, 1st MARINELIVE Workshop on
Electric Machines & Power Converters, January 11-12, 2012, Athens, Greece
[5] National Instruments DAQPad 6015 user’s manual.
[6] MITSUBISHI Transistorised inverter, FR-E500 Instruction manual, 2000.